7.52 .fill repeat , size , value

repeat, size and value are absolute expressions.
This emits repeat copies of size bytes. Repeat
may be zero or more. Size may be zero or more, but if it is
more than 8, then it is deemed to have the value 8, compatible with
other people's assemblers. The contents of each repeat bytes
is taken from an 8-byte number. The highest order 4 bytes are
zero. The lowest order 4 bytes are value rendered in the
byte-order of an integer on the computer as is assembling for.
Each size bytes in a repetition is taken from the lowest order
size bytes of this number. Again, this bizarre behavior is
compatible with other people's assemblers.

size and value are optional.
If the second comma and value are absent, value is
assumed zero. If the first comma and following tokens are absent,
size is assumed to be 1.